168 Marine Macro- and Microalgae: An Overview
and promote the growth of red cells. Lutein and zeaxanthin exist both in Chlorella biomass, and play an
important role on the eye vision system’s maintenance, preventing macular degeneration. Beta-carotene
and astaxanthin are powerful antioxidants also present, and are used in competition animals to prevent
oxidation in the body caused by reactive oxygen species.
Effect of processing on the digestibility of microalgae
The cell walls accounts for ca. 10% of the algal dry matter, and although its composition is strain-specific,
it contains cellulose in most of the species. This cellulosic cell wall is not digestible for non-ruminants,
and therefore presents a problem in digesting, or more broadly, utilizing algal biomass. In fact, effective
disrupting treatments are necessary in order to allow the access of digestive enzymes to the algal protein
and remaining components. Apart from Spirulina, all the commercially important algae (Chlorophyceae,
Rodophyceae) present an indigestible cell wall, which obliges a disruption process to be performed. Such
disruptive process can be performed by physical (e.g., boiling, drying) or chemical methods (Becker
2004).
Toxicological issues
In order to prove their safety, unconventional food sources have to fulfil a series of toxicological tests
for the presence of biogenic (toxic compounds synthesized by the algae or formed by decomposition of
metabolic products) or non-biogenic toxins (environmental contaminants, which can usually be avoided
by proper cultivation techniques and selection of cultivation places free of pollution).
Biogenic toxins include nucleic acids and other algal toxins. One of the very few constituents present
in all living organisms and hence in algae, and which under certain circumstances may be counted as
toxin, are nucleic acids (RNA and DNA). They are the sources of purines, which may lead to an increase
of plasma uric acid concentration in humans. Consequently, the recommended daily intake of nucleic
acids from unconventional sources should not exceed 2.0 g per day, which corresponds to 20 g of algae
per day. Nevertheless, these possible problems were reported for humans, and there are no studies of this
possible toxic effect on animals (Becker 2004).
Although poisoning of livestock and other animals due to toxic blooms of algae frequently occurs,
algal strains associated with this phenomenon are predominantly cyanobacteria. There are no reports of
toxicity cases in connection with mass-cultured algae, and numerous chemical and toxicity studies, as
well as feeding trials carried on along the years never revealed any pathological symptoms due to algal
toxins.
Concerning non-biogenic toxins, most problematic issues are related with the possible presence of
heavy metals and polycyclic aromatic compounds in the algal biomass. There are no characteristic levels
of these compounds in microalgae, they simply depend on the environmental conditions prevailing but
can be completely eliminated through microalgal cultivation in closed photobioreactors.
Microalgae as ingredients for animal feeds
About 30% of the current world annual production of Spirulina is sold as ingredient for animal feed
applications. Although most of its positive effects rely in nutritional field (e.g., increased growth rate,
colour enhancement, and general tissue quality), the fact that growth rates are improved, even at 0.1%
Spirulina supplementation, suggest the presence of substances that may mimic the effects of or stimulate
production of growth hormones. Within these non-nutritional effects, the most promising one may be an
immune enhancement effect due to the antiviral and anti-bacterial properties presented by Spirulina or its
extracts, especially during the early stages of animal life (Belay et al. 1996).
The use of microalgae as general animal feed ingredient is more recent when compared with their
utilization in human food. Within this new market, a growing sector is the utilization of microalgae in
aquaculture; although aquaculture already successfully uses several microalgal species as an essential
component of the live food chain in the early development phases of fish production, the potential of
and promote the growth of red cells. Lutein and zeaxanthin exist both in Chlorella biomass, and play an
important role on the eye vision system’s maintenance, preventing macular degeneration. Beta-carotene
and astaxanthin are powerful antioxidants also present, and are used in competition animals to prevent
oxidation in the body caused by reactive oxygen species.
Effect of processing on the digestibility of microalgae
The cell walls accounts for ca. 10% of the algal dry matter, and although its composition is strain-specific,
it contains cellulose in most of the species. This cellulosic cell wall is not digestible for non-ruminants,
and therefore presents a problem in digesting, or more broadly, utilizing algal biomass. In fact, effective
disrupting treatments are necessary in order to allow the access of digestive enzymes to the algal protein
and remaining components. Apart from Spirulina, all the commercially important algae (Chlorophyceae,
Rodophyceae) present an indigestible cell wall, which obliges a disruption process to be performed. Such
disruptive process can be performed by physical (e.g., boiling, drying) or chemical methods (Becker
2004).
Toxicological issues
In order to prove their safety, unconventional food sources have to fulfil a series of toxicological tests
for the presence of biogenic (toxic compounds synthesized by the algae or formed by decomposition of
metabolic products) or non-biogenic toxins (environmental contaminants, which can usually be avoided
by proper cultivation techniques and selection of cultivation places free of pollution).
Biogenic toxins include nucleic acids and other algal toxins. One of the very few constituents present
in all living organisms and hence in algae, and which under certain circumstances may be counted as
toxin, are nucleic acids (RNA and DNA). They are the sources of purines, which may lead to an increase
of plasma uric acid concentration in humans. Consequently, the recommended daily intake of nucleic
acids from unconventional sources should not exceed 2.0 g per day, which corresponds to 20 g of algae
per day. Nevertheless, these possible problems were reported for humans, and there are no studies of this
possible toxic effect on animals (Becker 2004).
Although poisoning of livestock and other animals due to toxic blooms of algae frequently occurs,
algal strains associated with this phenomenon are predominantly cyanobacteria. There are no reports of
toxicity cases in connection with mass-cultured algae, and numerous chemical and toxicity studies, as
well as feeding trials carried on along the years never revealed any pathological symptoms due to algal
toxins.
Concerning non-biogenic toxins, most problematic issues are related with the possible presence of
heavy metals and polycyclic aromatic compounds in the algal biomass. There are no characteristic levels
of these compounds in microalgae, they simply depend on the environmental conditions prevailing but
can be completely eliminated through microalgal cultivation in closed photobioreactors.
Microalgae as ingredients for animal feeds
About 30% of the current world annual production of Spirulina is sold as ingredient for animal feed
applications. Although most of its positive effects rely in nutritional field (e.g., increased growth rate,
colour enhancement, and general tissue quality), the fact that growth rates are improved, even at 0.1%
Spirulina supplementation, suggest the presence of substances that may mimic the effects of or stimulate
production of growth hormones. Within these non-nutritional effects, the most promising one may be an
immune enhancement effect due to the antiviral and anti-bacterial properties presented by Spirulina or its
extracts, especially during the early stages of animal life (Belay et al. 1996).
The use of microalgae as general animal feed ingredient is more recent when compared with their
utilization in human food. Within this new market, a growing sector is the utilization of microalgae in
aquaculture; although aquaculture already successfully uses several microalgal species as an essential
component of the live food chain in the early development phases of fish production, the potential of